1988

Global Climate Changes as Forecast by Goddard Institute for Space Studies Three-Dimensional Model

J. Hansen, I. Fung, A. Lacis, D. Rind, S. Lebedeff, R. Ruedy, G. Russell & P. Stone

Observation and Context

Atmospheric greenhouse gases like carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons are gradually increasing due to human activities, while volcanic eruptions periodically inject cooling aerosols into the stratosphere. Past modeling studies only looked at instant doublings of carbon dioxide at equilibrium. However, real-world emissions grow gradually over time, meaning actual climate responses depend heavily on transient factors like ocean heat absorption. Understanding how greenhouse gases force climate perturbations over short decadal intervals is vital for future human planning.

Hypothesis

If a three-dimensional global climate model simulates gradual, time-dependent variations in trace gases and aerosols paired with a diffusive ocean model, then it can forecast the timing, magnitude, and geographical patterns of human-induced global warming while rising clearly above the baseline of natural unforced climate variability.

Experiment and Methodology

Researchers utilized the GISS 3D Model II, featuring an eight-by-ten-degree grid with nine atmospheric layers. The ocean model fixed horizontal heat transport at today’s rates but allowed vertical heat diffusion below the mixed layer. First, a one-hundred-year control run with fixed 1958 atmospheric levels measured natural climate variability. Second, starting in 1958, they ran experiments using three scenarios: Scenario A assumed exponential emissions growth, Scenario B assumed reduced linear growth, and Scenario C assumed a rapid freeze on emissions by the year 2000.

Results and Data

The control run showed unforced natural variability with a standard deviation of 0.11 degrees, establishing that a 0.4 degree warming represents a significant human-caused signal. Greenhouse warming becomes clearly identifiable during the 1990s across all scenarios, tracking three standard deviations above the 1950s baseline. Record interglacial warmth is reached in all cases, though long-term temperatures diverge wildly based on emissions choices. Clear warming appears earliest in low-latitude oceans, China, interior Asia, and polar zones. Furthermore, a near-term regional pattern emerged during the late 1980s and 1990s, creating more warming in the southeastern United States but relatively cooler conditions in Europe and the western United States. The model also clearly illustrated that stratospheric cooling occurs simultaneously with tropospheric warming, providing a unique fingerprint of greenhouse gas forcing.

Conclusion and Climate Impact

The hypothesis was supported, demonstrating that transient global warming can be successfully tracked over decades. Human-induced greenhouse warming will soon permanently alter global temperatures far faster than the shifts found in paleoclimate records. This rapid warming creates severe climate impacts because temperature zones will shift faster than ecosystems can naturally migrate. Crop yields will face nonlinear threats from an increased frequency of extreme heatwaves, and local populations will experience significant drops in their overall quality of life as extreme weather disturbances multiply.